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Date:   Tue, 22 Mar 2022 12:03:11 +0900
From:   Masami Hiramatsu <mhiramat@kernel.org>
To:     Padmanabha Srinivasaiah <treasure4paddy@gmail.com>
Cc:     Steven Rostedt <rostedt@goodmis.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Jonathan Corbet <corbet@lwn.net>, linux-doc@vger.kernel.org,
        Randy Dunlap <rdunlap@infradead.org>
Subject: Re: [PATCH v2 2/3] bootconfig: Support embedding a bootconfig file
 in kernel
Message-Id: <20220322120311.690f237b63ddfd9c0e4f78ec@kernel.org>
In-Reply-To: <20220321183500.GA4065@pswork>
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        <164724892075.731226.14103557516176115189.stgit@devnote2>
        <20220316191649.GA11547@pswork>
        <20220318101445.fdb151efe58c6c3a1c572500@kernel.org>
        <20220321183500.GA4065@pswork>
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On Mon, 21 Mar 2022 19:35:00 +0100
Padmanabha Srinivasaiah <treasure4paddy@gmail.com> wrote:

> Hello Masami Hiramatsu,
> 
> On Fri, Mar 18, 2022 at 10:14:45AM +0900, Masami Hiramatsu wrote:
> > On Wed, 16 Mar 2022 20:16:49 +0100
> > Padmanabha Srinivasaiah <treasure4paddy@gmail.com> wrote:
> > 
> > > Hello Masami Hiramatsu,
> > > 
> > > On Mon, Mar 14, 2022 at 06:08:41PM +0900, Masami Hiramatsu wrote:
> > > > This allows kernel developer to embed a default bootconfig file in
> > > > the kernel instead of embedding it in the initrd. This will be good
> > > > for who are using the kernel without initrd, or who needs a default
> > > > bootconfigs.
> > > > This needs to set two kconfigs: CONFIG_EMBED_BOOT_CONFIG=y and set
> > > > the file path to CONFIG_EMBED_BOOT_CONFIG_FILE.
> > > > 
> > > > Note that you still need 'bootconfig' command line option to load the
> > > > embedded bootconfig. Also if you boot using an initrd with a different
> > > > bootconfig, the kernel will use the bootconfig in the initrd, instead
> > > > of the default bootconfig.
> > > > 
> > > > Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> > > > ---
> > > >  include/linux/bootconfig.h |   10 ++++++++++
> > > >  init/Kconfig               |   21 +++++++++++++++++++++
> > > >  init/main.c                |   13 ++++++++-----
> > > >  lib/.gitignore             |    1 +
> > > >  lib/Makefile               |   12 ++++++++++++
> > > >  lib/bootconfig.c           |   23 +++++++++++++++++++++++
> > > >  6 files changed, 75 insertions(+), 5 deletions(-)
> > > > 
> > > > diff --git a/include/linux/bootconfig.h b/include/linux/bootconfig.h
> > > > index a4665c7ab07c..5dbda5e3e9bb 100644
> > > > --- a/include/linux/bootconfig.h
> > > > +++ b/include/linux/bootconfig.h
> > > > @@ -289,4 +289,14 @@ int __init xbc_get_info(int *node_size, size_t *data_size);
> > > >  /* XBC cleanup data structures */
> > > >  void __init xbc_exit(void);
> > > >  
> > > > +/* XBC embedded bootconfig data in kernel */
> > > > +#ifdef CONFIG_EMBED_BOOT_CONFIG
> > > > +char * __init xbc_get_embedded_bootconfig(size_t *size);
> > > > +#else
> > > > +static inline char *xbc_get_embedded_bootconfig(size_t *size)
> > > > +{
> > > > +	return NULL;
> > > > +}
> > > > +#endif
> > > > +
> > > >  #endif
> > > > diff --git a/init/Kconfig b/init/Kconfig
> > > > index e9119bf54b1f..70440804874d 100644
> > > > --- a/init/Kconfig
> > > > +++ b/init/Kconfig
> > > > @@ -1357,6 +1357,27 @@ config BOOT_CONFIG
> > > >  
> > > >  	  If unsure, say Y.
> > > >  
> > > > +config EMBED_BOOT_CONFIG
> > > > +	bool "Embed bootconfig file in the kernel"
> > > > +	depends on BOOT_CONFIG
> > > > +	default n
> > > > +	help
> > > > +	  Embed a bootconfig file given by EMBED_BOOT_CONFIG_FILE in the
> > > > +	  kernel. Usually, the bootconfig file is loaded with the initrd
> > > > +	  image. But if the system doesn't support initrd, this option will
> > > > +	  help you by embedding a bootconfig file while building the kernel.
> > > > +
> > > > +	  If unsure, say N.
> > > > +
> > > > +config EMBED_BOOT_CONFIG_FILE
> > > > +	string "Embedded bootconfig file path"
> > > > +	default ""
> > > > +	depends on EMBED_BOOT_CONFIG
> > > > +	help
> > > > +	  Specify a bootconfig file which will be embedded to the kernel.
> > > > +	  This bootconfig will be used if there is no initrd or no other
> > > > +	  bootconfig in the initrd.
> > > > +
> > > >  choice
> > > >  	prompt "Compiler optimization level"
> > > >  	default CC_OPTIMIZE_FOR_PERFORMANCE
> > > > diff --git a/init/main.c b/init/main.c
> > > > index 421050be5039..3803bf2e22ea 100644
> > > > --- a/init/main.c
> > > > +++ b/init/main.c
> > > > @@ -265,7 +265,7 @@ static int __init loglevel(char *str)
> > > >  early_param("loglevel", loglevel);
> > > >  
> > > >  #ifdef CONFIG_BLK_DEV_INITRD
> > > > -static void * __init get_boot_config_from_initrd(u32 *_size)
> > > > +static void * __init get_boot_config_from_initrd(size_t *_size)
> > > >  {
> > > >  	u32 size, csum;
> > > >  	char *data;
> > > > @@ -411,12 +411,15 @@ static void __init setup_boot_config(void)
> > > >  	static char tmp_cmdline[COMMAND_LINE_SIZE] __initdata;
> > > >  	const char *msg;
> > > >  	int pos;
> > > > -	u32 size;
> > > > +	size_t size;
> > > >  	char *data, *err;
> > > >  	int ret;
> > > >  
> > > >  	/* Cut out the bootconfig data even if we have no bootconfig option */
> > > >  	data = get_boot_config_from_initrd(&size);
> > > > +	/* If there is no bootconfig in initrd, try embedded one. */
> > > > +	if (!data)
> > > > +		data = xbc_get_embedded_bootconfig(&size);
> > > >  
> > > >  	strlcpy(tmp_cmdline, boot_command_line, COMMAND_LINE_SIZE);
> > > >  	err = parse_args("bootconfig", tmp_cmdline, NULL, 0, 0, 0, NULL,
> > > > @@ -435,8 +438,8 @@ static void __init setup_boot_config(void)
> > > >  	}
> > > >  
> > > >  	if (size >= XBC_DATA_MAX) {
> > > > -		pr_err("bootconfig size %d greater than max size %d\n",
> > > > -			size, XBC_DATA_MAX);
> > > > +		pr_err("bootconfig size %ld greater than max size %d\n",
> > > > +			(long)size, XBC_DATA_MAX);
> > > >  		return;
> > > >  	}
> > > >  
> > > > @@ -449,7 +452,7 @@ static void __init setup_boot_config(void)
> > > >  				msg, pos);
> > > >  	} else {
> > > >  		xbc_get_info(&ret, NULL);
> > > > -		pr_info("Load bootconfig: %d bytes %d nodes\n", size, ret);
> > > > +		pr_info("Load bootconfig: %ld bytes %d nodes\n", (long)size, ret);
> > > >  		/* keys starting with "kernel." are passed via cmdline */
> > > >  		extra_command_line = xbc_make_cmdline("kernel");
> > > >  		/* Also, "init." keys are init arguments */
> > > > diff --git a/lib/.gitignore b/lib/.gitignore
> > > > index e5e217b8307b..30a2a5db7033 100644
> > > > --- a/lib/.gitignore
> > > > +++ b/lib/.gitignore
> > > > @@ -6,3 +6,4 @@
> > > >  /oid_registry_data.c
> > > >  /test_fortify.log
> > > >  /test_fortify/*.log
> > > > +/default.bconf
> > > > diff --git a/lib/Makefile b/lib/Makefile
> > > > index 300f569c626b..8183785ee99d 100644
> > > > --- a/lib/Makefile
> > > > +++ b/lib/Makefile
> > > > @@ -279,6 +279,18 @@ $(foreach file, $(libfdt_files), \
> > > >  	$(eval CFLAGS_$(file) = -I $(srctree)/scripts/dtc/libfdt))
> > > >  lib-$(CONFIG_LIBFDT) += $(libfdt_files)
> > > >  
> > > > +ifeq ($(CONFIG_EMBED_BOOT_CONFIG),y)
> > > > +# Since the specified bootconfig file can be switched, we forcibly update the
> > > > +# default.bconf file always.
> > > > +$(obj)/default.bconf: FORCE
> > > > +	$(call cmd,defbconf)
> > > > +
> > > > +quiet_cmd_defbconf = GEN     $@
> > > > +      cmd_defbconf = cat < /dev/null $(CONFIG_EMBED_BOOT_CONFIG_FILE) > $@
> > > > +clean-files	+= default.bconf
> > > > +$(obj)/bootconfig.o: $(obj)/default.bconf
> > > > +endif
> > > > +
> > > >  lib-$(CONFIG_BOOT_CONFIG) += bootconfig.o
> > > >  
> > > >  obj-$(CONFIG_RBTREE_TEST) += rbtree_test.o
> > > > diff --git a/lib/bootconfig.c b/lib/bootconfig.c
> > > > index 74f3201ab8e5..3a3bf3a208e3 100644
> > > > --- a/lib/bootconfig.c
> > > > +++ b/lib/bootconfig.c
> > > > @@ -12,6 +12,29 @@
> > > >  #include <linux/kernel.h>
> > > >  #include <linux/memblock.h>
> > > >  #include <linux/string.h>
> > > > +
> > > > +#ifdef CONFIG_EMBED_BOOT_CONFIG
> > > > +asm (
> > > > +"	.pushsection .init.data, \"aw\"			\n"
> > > > +"	.global embedded_bootconfig_data		\n"
> > > > +"embedded_bootconfig_data:				\n"
> > > > +"	.incbin \"lib/default.bconf\"			\n"
> > > > +"	.global embedded_bootconfig_data_end		\n"
> > > > +"embedded_bootconfig_data_end:				\n"
> > > > +"	.popsection					\n"
> > > > +);
> > > > +
> > > > +extern __visible char embedded_bootconfig_data[];
> > > > +extern __visible char embedded_bootconfig_data_end[];
> > > > +
> > > > +char * __init xbc_get_embedded_bootconfig(size_t *size)
> > > > +{
> > > > +	*size = embedded_bootconfig_data_end - embedded_bootconfig_data;
> > > > +	return (*size) ? embedded_bootconfig_data : NULL;
> > > > +}
> > > > +
> > > > +#endif
> > > > +
> > > >  #else /* !__KERNEL__ */
> > > >  /*
> > > >   * NOTE: This is only for tools/bootconfig, because tools/bootconfig will
> > > >
> > > 
> > > Thanks tested the implemation, it works as expected.
> > 
> > Great!
> > 
> > > 
> > > Also noted that a change in default.bconf requries a clean build, is it
> > > expected behaviour?
> > 
> > default.bconf will be always updated if CONFIG_EMBED_BOOT_CONFIG=y. So you can
> > do incremental build. (I tested it with the incremental build environment)
> >
> 
> Thanks, your observation made me to further experiment ther incremental build.
> 
> Below are the observations I have:
> 
> When I use GCC for a build; yes, the modified default.conf was observed on
> the target.
> 
> But when I use clang; either with FULL or THIN LTO, the modified
> default.conf doesnt get reflected on the target.

Hmm, curious. So you just add 'CC=clang' on the make command line, right?
Can you confirm that following line in your build log,

  GEN     lib/default.bconf

and the timestamp of lib/bootconfig.o is built after lib/default.bconf file?

And is that related to CONFIG_LTO? What happen if CONFIG_LTO=n?

Thank you,

> 
> PS: Using: GCC version 8.2.1 20180802, LLVM version 13.0.2git.
> 
> Thank you,
> Padmanabha.S
> > Thank you,
> > 
> > > 
> > > Thanks and Regards,
> > > Padmanabha.S
> > 
> > 
> > -- 
> > Masami Hiramatsu <mhiramat@kernel.org>


-- 
Masami Hiramatsu <mhiramat@kernel.org>